1. Field of the Invention
The present invention relates to a plate-shaped member having a recess, a method of manufacturing the plate-shaped member, and a press die for forming the recess. More particularly, the present invention relates to a plate-shaped member having a recess for electronic parts which recess is formed without bending a metallic plate, a method of manufacturing such plate-shaped member, and a press die, for forming the recess, having a punch for forming the recess on the metallic plate by means of press forming and a die, on which the metallic plate is put, arranged opposed to the punch.
2. Description of the Related Art
As illustrated in FIG. 19, which is referred to hereinafter to explain a semiconductor device to which the present invention can be applied, a semiconductor device containing a cap-shaped heat dissipation plate adhered to semiconductor element is mounted on a circuit board.
Not only the semiconductor device but also other various electronic parts such as a chip capacitor can be mounted on the circuit board. Therefore, the upper surface and lower surface of the heat dissipation plate, the profile of which is formed into a cup-shape, must be flat.
Generally, the cap-shaped heat dissipation plate has been produced from a metallic plate by press forming the metallic plate. The press forming, as disclosed in the xe2x80x9cprior artxe2x80x9d section of Japanese Unexamined Patent Publication (Kokai) No. 2000-42642 and shown in FIGS. 1A to 1C of this application for reference, comprises the steps of providing a metallic plate 90 as a raw material as shown in FIG. 1A, and then placing the metallic plate 90 on a die 91 of the pressing machine, followed by pressing the metallic plate 90 from a side of the surface 90a of the plate 90 with a pressing punch 92 as shown in FIG. 1B. As a result, as is shown in FIG. 1C, a recess 93 is formed on the surface 90a of the plate 90. Further, a bottom portion 90c having the predetermined thickness is formed in a bottom surface of the recess 93. A semiconductor element (not shown) is contained in a space 95 formed by the recess 93.
In the press forming illustrated in FIGS. 1A to 1C, a material of the recess 93 can move, in the direction of the arrows shown in FIG. 1B, in the metallic plate 90 during pressing the plate 90 with the punch 92. Thus, as is shown in FIG. 1C, a rounded corner part 93a is produced as a result of sagging of the material in the opening ends of the recess 93, along with the formation of a tapered inner wall 93b. Further, the metallic plate 90 is warped, because the outer ends are lifted at an angle xcex8 due to the stress applied to the plate 90 by the punch 92.
Due to the above problems, it is difficult for the prior art press forming method to ensure that the inside and outside of the heat dissipation plate are formed completely flat. Note that Japanese Kokai NO. 2000-42642 teaches a method for forming a recess, in a metallic plate, with a recess having a perpendicular inner wall. However, it is still difficult to produce a heat dissipation plate having completely flat inside and outside surfaces.
To avoid the above problems, there has been suggested a cutting method, in place of the press forming method, in the formation of the cap-shaped heat dissipation plate. That is, as illustrated in FIG. 2, a metallic plate 90 is cut to form a recess 93 which defines a space 95 for receiving a semiconductor element or other part (not shown), followed by cutting off the unnecessary end portions at the cutting line, shown by a dotted line in the drawing, to obtain a cap-shaped heat dissipation plate having the predetermined configuration and size. As illustrated, the recess 93 has a perpendicular inner wall 93b, along with a bottom portion 90c with a predetermined thickness.
When the recess is formed in the metallic plate by cutting as described above, the inside and outside of the finally obtained cap-shaped heat dissipation plate can be made flat. Note, however, work time necessary for the process of forming the heat dissipation plate is mainly determined by the process of forming the recess on the metallic plate by means of cutting and it is very difficult to enhance the cutting speed.
Further, in order to form the cap-shaped heat dissipation plate by cutting, it is necessary to provide a metallic plate, the thickness of which is at least the same as the thickness between the upper end and the lower end of the side wall 90d which defines the heat dissipation plate. In order to satisfy this requirement, it is generally necessary to use a metallic plate, the thickness of which is much larger than the thickness of the side wall 90d, thus the material cost is increased.
If it were possible to produce the cup-shaped heat dissipation plate by using press forming, the speed of producing the heat dissipation plate could be remarkably increased, and further a metallic plate could be used which is thinner than a metallic plate used in the production of the cap-shaped heat dissipation plate by cutting.
The present invention is directed to solve the prior art problems discussed above.
One object of the present invention is to provide a plate-shaped member, having a recess, the inside and outside of which are formed as flat as possible by using press forming, particularly useful for electronic parts.
Another object of the present invention is to provide an improved method of manufacturing the plate-shaped member, having a recess, by press forming.
Still another object of the present invention is to provide a press die for forming recesses which is useful in the production of the plate-shaped member, having a recess, from a metallic plate.
The above objects and other objects of the present invention will be easily understood from the following detailed description of the present invention.
The present inventors have made investigation into the above problems, and as a result, they have found the following facts and accomplished the present invention. That is, if the fabrication is conducted on a metallic plate to form a first recess and, on the bottom face of the thus formed first recess, a second recess is formed by punching, while metal extruded by punching at this time is protruded in such a manner that a bottom portion of the first recess between the first and the second recess is protruded to form a protuberance portion, followed by making an upper face of this protuberance portion flat, the thickness, between the upper end and the lower end, of the side wall of the produced recess can be made larger than the thickness of the metallic plate on which press forming is applied.
In one aspect thereof, the present invention provides a plate-shaped member having a recess, defined by a bottom wall portion and a side wall portion extending from a peripheral end of the bottom wall portion, formed by press forming a metallic plate without bending the same, characterized in that an upper surface and lower surface of the side wall portion and bottom wall portion each has a flat and parallel surface, the thickness of the bottom wall portion is smaller than the thickness of the metallic plate (before press forming), and the thickness, between an upper end surface and a lower end surface, of the side wall portion is larger than the thickness of the metallic plate (before press forming).
The plate-shaped members with recesses according to the present invention can be advantageously used for a variety of parts based on the flat inside and outside of the recesses, preferably as electronic parts, more preferably as a cap-shaped heat dissipation plates for semiconductor elements in semiconductor devices.
Further, in another aspect thereof, the present invention provides a method of manufacturing a plate-shaped member having a recess, defined by a bottom wall portion and a side wall portion extending from a peripheral end of the bottom wall portion, by press forming a metallic plate without bending the same, comprising the steps of:
forming a first recess in a metallic plate, the opening area of which is larger than the opening area of the recess, by fabricating the metallic plate with a first punch;
forming a second recess in a bottom wall portion of the first recess by using a press die comprising a second punch, the cross-sectional area of which is equal to the opening area of the recess, and a die having, on a face opposed to a forward end face of the second punch, a recess into which a protruding portion of the metallic plate produced by the formation of the first recess is inserted, while forming a protuberance portion in such a manner that the thickness of the bottom wall portion of the second recess is made to be smaller than the thickness of the bottom wall portion of the first recess, and the bottom wall portion of the first recess, between the first and the second recesses, is protruded so that the thickness between the upper surface and the lower surface of the protuberance portion can be larger than the thickness of the metallic plate;
forming an upper surface of the protuberance portion into a flat surface while retaining the flatness of the upper surface and lower surface of the side wall portion and the bottom wall portion defining the second recess and the thickness between the upper surface and the lower surface, of the protuberance portion which is larger than the thickness of the metallic plate; and
cutting the protuberance section to a predetermined width.
In the manufacturing process of the plate-shaped member according to the present invention, it is preferred that a side wall portion of the recess is formed after a flat upper surface was formed in the protuberance section in the cutting step.
Furthermore, in another aspect thereof, the present invention provides a press die for forming a recess in a metallic plate for the production of a plate-shaped member having a recess, the recess being defined by a bottom wall portion and a side wall portion extending from a peripheral end of the bottom wall portion, which press die comprises a punch for forming a recess on the metallic plate by press forming, and a die opposed to the punch, on which die the metallic plate is put, and in which press die, at least one of the forward end face of the punch and the opposed face of the die opposed to the forward end face of the punch has a protruding section of cone, truncated cone, polygonal pyramid, truncated polygonal pyramid, hemisphere or truncated hemisphere.
The present invention can be preferably applied to the production of electronic parts, particularly heat dissipation plates, for semiconductor elements. In the production of the plate-shaped member having a recess, when the absorbing section such as a slit for absorbing an elongation created on the work face of the metallic plate during the press forming is formed close to a portion to be press-formed on the metallic plate before the formation of the first recess, distortion and deformation of the profile of the resulting recess can be prevented.
Further, according to the present invention, on the bottom wall of the first recess formed by press shaping of the metallic plate, the second recess is further formed by punching, and, at the same time, metal extruded by punching is absorbed when the bottom wall of the first recess between the first and the second recesses is protruded. Therefore, it is possible to form a protuberance section in which the thickness between the upper and lower surfaces is larger than the thickness of the metallic plate (before press forming). Therefore, when the upper surface of this protuberance section is made flat while the thickness between the upper and lower surfaces of the protuberance section is being kept larger than the thickness of the metallic plate (before press forming), the thickness between the upper and lower end surfaces of the side wall section of the recess can be formed larger than the thickness of the metallic plate (before press forming).
Furthermore, since the upper surface of the protuberance section is made flat while the inside and the outside of the second recess are being kept flat, the side wall and the bottom wall of the recess formed in the finally obtained plate-shaped member can be formed flat.